Presently, data communication equipment ("DCE"), such as modems, for example, are used to transport digital data between data terminal equipment such as personal computers, workstations, and the like, over channels such as telephone lines. Typically, the communication signal includes digital data in the form of a carrier signal that is modulated by a predetermined transmit constellation of signal points at a signaling rate. Hereafter the signaling rate will also be known as the symbol rate. A set of signal points taken from the transmit constellation represents a digital code or value to be transported. At the local DCE, a carrier signal is thus modulated with the set of constellation signal points corresponding to the digital code or value to be transported over the channel. Impedance mismatch between the remote DCE and the channel can cause reflections, or echoes, back into the receiver of the local DCE. Echoes into the local receiver caused by impedance mismatch at the remote end are known as far end echoes. In addition, the channel may introduce frequency offset which will alter the carrier frequency of signals which pass through it. This frequency offset is known as far end echo phase roll. The local DCE will attempt to generate an exact replica of this far end echo and subtract, or cancel, it from the local receiver. If the effect of the phase roll is not considered, then an exact replica cannot be constructed, and the result will be a reduction in the maximum data rate supported by the local DCE receiver. Therefore, before the digital data is transported, the far end echo phase roll must be determined and tracked.
As a result, there is a need to provide a DCE with the mechanism for determining and tracking the phase roll of the far end echo.